1. Field of the Invention
The present invention is applied to a fuel injection system of diesel engines, the injection system being a common rail fuel injection system; thereby, a high pressure pump pressurizes fuel oil, and the pressurized fuel oil is sent to and accumulated in the common rail (an accumulator volume); a prescribed amount of the highly pressurized fuel oil accumulated in the common rail is injected into each cylinder of the engine, through the fuel injector (a fuel injection valve), at predetermined timing or timings for predetermined duration of time; the present invention relates to a pressure fluctuation control device for controlling the pressure fluctuation in the upstream side of a common rail in the common rail fuel injection system (an accumulator injection system).
2. Background of the Invention
In the common rail (an accumulator volume) fuel injection device depicted in FIGS. 5(A), 5(B), 6 and 7, a high pressure pump 3 pressurizes fuel oil; and, the pressurized fuel oil is sent to and accumulated in a common rail (an accumulator volume) 1; a prescribed amount of the highly pressurized fuel oil accumulated in the common rail is injected into each cylinder at predetermined timing or timings for predetermined duration of time, per each cylinder, through a fuel injector 6 (a fuel injection valve) corresponding to the cylinder, the fuel injector communicating with the common rail through a fuel injection pipe 12 corresponding to the cylinder; thereby, the predetermined timing and the predetermined duration are determined on the basis of the engine operation condition and the firing timing of the cylinder.
As shown in FIG. 5(A), a plurality of cylinders (3 cylinders in this case) is provided in the high pressure pump 3; each cylinder (of the pump 3) pressurizes the fuel oil; at the fuel outlet of each cylinder, a check valve 10 is provided so as to open and close the fuel passage of the check valve; after passing through the check valves 10, the high pressure fuel oil is sent to a plurality of pressure accumulation rooms 16 (3 rooms in this case); in the pressure accumulation rooms 16, the surging pressures (or pressure fluctuations) regarding the delivery pressure of the fuel delivered by the pump 3 are relieved; then, the fuel oil is guided into the common rail 1 through a plurality of high pressure pipes 23 (3 pipes in this case).
Since the configuration as to the downstream side of the fuel-flow from the common rail toward each cylinder of the engine is a configuration of public knowledge, detailed explanations are omitted; however, it is noted that a prescribed amount of the highly pressurized fuel oil accumulated in the common rail is injected into each cylinder of the engine, at predetermined timing or timings (according to each cylinder's injection timing) predetermined duration of time per cylinder of the engine, through a fuel injector 6 (a fuel injection valve) corresponding to the cylinder of the engine; the fuel injector communicates with the common rail through a fuel injection pipe 12 in response to the corresponding cylinder of the engine; thereby, the predetermined timing (injection timing) and the predetermined duration are determined on the basis of the engine operation condition and the firing timing of the cylinder.
Further, as shown in FIG. 7, the multiple check valves 10 are provided so that the number of check valves is equal to the number of cylinders in the high pressure pump 3 that delivers high pressure fuel oil; while the pressure of the pressurized fuel oil is not lower than a certain pressure established by a spring 10b and a valve body 10a that are housed in a spring chamber 10c, the high pressure fuel oil can stream toward an upstream side 10e; on the other hand, the check valve 10 prevents the high pressure fuel oil from back-flowing to a delivery chamber 3b from the upstream side 10e. 
The check valve 10 is provided with a case 10f housing the components of the check valve 10; the case 10 is fastened to a case (a high pressure pump body) 3d of the high pressure pump 3, by use of a plurality of bolts 10d. 
The high pressure fuel oil passing through the check valve 10 is sent to the common rail 1.
In addition, the high pressure pump 3 supplies the high pressure fuel oil toward the check valve 10, by pressurizing the fuel oil in the delivery chamber 3b through the reciprocating movements which a plunger 3a performs slidably in the case 3d, the reciprocating movements being driven by a tappet 3c. 
In FIG. 5(B), the pressure accumulation rooms 16 in FIG. 5(A) are integrated into a pressure accumulation room 16a of an integral type, the integration being performed per a plurality of cylinders (3 cylinders in this case) of the high pressure pump 3; thus, the volume of the pressure accumulation rooms 16 is increased into the volume of the pressure accumulation room 16a; as a result, the effect on the surging pressure reduction is enhanced.
The other configuration in FIG. 5(B) is the same as that in FIG. 5(A); and, the check valve 10 depicted in FIG. 5(A) and the check valve 10 depicted in FIG. 5(B) have the same configuration as depicted in FIG. 7; the same component is quoted with the same numeral.
The patent reference JP3531896 discloses a common rail injection system in which a secondary common rail 10 (a sub-common-rail) is provided at an end side of the common rail 5, the secondary common rail 10 being connected to the common rail 5 through a high pressure pipe (other than the fuel injection pipes) and an open-close valve (an on-off valve) 11 on a part way of the high pressure pipe.
The configuration depicted in FIG. 6 is similar to that depicted in FIG. 5(A); however, in the case of FIG. 6, the length of each high pressure pipe 23b that connects each pressure accumulation room to the common rail 1 is reduced in comparison with the case of FIG. 5(A); thus, the reduction of the surging pressures is aimed at.
The other configuration in FIG. 6 is the same as that in FIG. 5(A); and, the check valve 10 depicted in FIG. 5(A) and the check valve 10 depicted in FIG. 6 have the same configuration as depicted in FIG. 7; the same component is quoted with the same numeral.
As described above, in the common rail (an accumulator) fuel injection device, the high pressure pump 3 pressurizes fuel oil; and, the pressurized fuel oil is sent to and accumulated in the common rail (the accumulator volume) 1; a prescribed amount of the highly pressurized fuel oil accumulated in the common rail is injected into each cylinder of the engine at predetermined timing or timings for predetermined duration of time, per engine cylinder, through the fuel injector 6 (the fuel injection valve) corresponding to the cylinder; thereby, the predetermined timing or timings and the predetermined duration are determined on the basis of the engine operation condition and the firing timing of the cylinder.
On the other hand, it is an urgent matter to restrain the pumping pulsation (pressure pulsation) at every cylinder of the high pressure pump 3 that comprises a plurality of cylinders; each cylinder pressurizes the fuel oil; the check valve 10 is provided at the outlet of each cylinder of the pump 3 so as to open and close the fuel passage of the check valve; further, it is also an urgent matter to reduce the surging pressure that is generated in opening and closing the check valve 10. To be more specific, in a case of the small engines for vehicle use or generator use, the engines have to be compact and are strongly required to restrain the pumping pulsations and the surging pressures.
In view of the requirement as described above, the means as depicted in FIGS. 5(A), 5(B), 6 and 7 are conventionally provided; however, according the fuel injection device of FIG. 5(A), as many (3 cylinders in this case) pressure accumulation rooms 16 are provided as there are cylinders of the high pressure pump 3; accordingly, the volume of each pressure accumulation room 16 has to be large enough to satisfactorily reduce the pumping pulsations and the surging pressures; thus, the size of the high pressure pump 3 has to be upsized. Further, according the fuel injection device of FIG. 5(B), the pressure accumulation rooms 16 are integrated into a pressure accumulation room 16a of an integral type so as to reduce the pumping pulsations and the surging pressures; thereby, the shape of the accumulation room 16a of an integral type becomes complicated and upsized; moreover, the prevention against the leakage of the high pressure fuel oil becomes difficult in view of the design of the accumulation room 16a; and, the degree of accuracy in finishing the accumulation room 16a has to be enhanced.
Further, according the fuel injection device of FIG. 6, the length of each high pressure pipe 23b that connects each pressure accumulation room to the common rail 1 is reduced in comparison with the corresponding length in the conventional fuel injection device; thus, the reduction of the inertia mass regarding the fuel oil in the pipe 23 is aimed at, in order to reduce the pumping pulsations and the surging pressures. However, it is often difficult to reduce the length of the high pressure pipe 23b because of the constraint conditions regarding the system layout (the arrangements of the common rail injection system).
As described thus far, in the accumulator injection device provided with the common rail 1, multiple cylinders of the high pressure pump 3 pressurizes the fuel oil; at the fuel outlet of each cylinder, the check valve 10 is provided so as to open and close the fuel passage of the check valve. In a case where the pumping pulsations generated at each cylinder as well as the surging pressures generated by the on-off movements of the check valve 10 is reduced in the pressure accumulation room 16 or 16a on the upstream side of the common rail 1, the volume of the pressure accumulation room 16 or 16a on the upstream side of the common rail 1 has to be large enough in order to satisfactory reduce the pumping pulsations and the surging pressures.